This invention relates to an internal combustion engine and, more particularly, to an improved induction system for such an engine.
Recently it has been proposed to improve the low speed performance of an internal combustion engine without sacrificing high power output, by providing a relatively small cross-sectional area, auxiliary induction passage that delivers a substantial portion of the low speed charge requirements to the engine chambers. The use of such an auxiliary induction system has been found to significantly improve low speed running by increasing turbulence and, accordingly, flame propagation in the chambers at the time of combustion. In accordance with this invention, several improvements are provided for this general type of induction system.
One particularly critical operating period for an internal combustion engine is under cold starting and cold running conditions. Under these conditions, the fuel delivery to the combustion chambers is uneven and must be normally designed to be over-rich so as to insure good running. The use of such over-rich mixtures, however, deteriorates both fuel economy and exhaust emission control.
The use of the small cross-sectional auxiliary induction system, previously described, has been found to improve cold running and warm-up operation of the engine. It is, therefore, a first object of this invention to provide an induction system that further improves cold starting and cold running performance of an internal combustion engine.
One method of improving such cold starting and cold running performance employs the use of a fuel injection nozzle in the auxiliary induction system for providing cold starting and cold running enrichment. By introducing the enriched mixture directly into the auxiliary induction system, fuel vaporization and distribution is significantly improved, due to the high velocity of air flow through the auxiliary induction system, even at low speeds and during cranking. If multiple cylinders are employed, one cold starting fuel injection enrichment nozzle may be employed for several cylinders, as the nozzle discharges into a common supply passage of the auxiliary induction system.
In accordance with another feature and object of the invention, engine warm-up is accelerated by introducing excess air into the auxiliary induction system under cold running conditions. This excess air further improves the amount of fuel vaporization and increases the engine speed, so as to promote faster warm-up. As a result, cold running enrichment may be stopped at an earlier time to improve both efficiency and exhaust emission control.
In accordance with still another feature or the invention, a more effective means for controlling idle air flow is employed from those previously known. Normally it has been the practice to control air flow through an induction system by the use of a butterfly type valve that is rotatably mounted in a portion of the induction passage. The amount of air flow through the induction passage at idle is determined by an initial setting of the throttle valve to something other than its fully closed position. This introduces variations in adjustment and has other disadvantages.
It is, therefore, a yet further object of this invention to provide an improved structure for controlling idle air flow.